Medicated aerosol dispensers are generally well known in the art, such as anti-asthmatic medication dispensers providing medication from a propellant-charged canister through a device for creating aerosol including a mouth piece. These devices generally created an aerosol having a spray with oversized liquid particles with a significant forward velocity which impacted the patient's mouth or lips when the inhaler was operated. There is no compact device which could deliver an aerosol from such a canister having droplets of one to three microns monodispersed size. A 10-centimeter (4-inch) spacer was typically attached to the inhaler in an attempt to provide uniform particle size, which did not succeed. These spacers produced a noncompace cumbersome inhaler with most of the medicine trapped in the device and not delivered to the patient.
Prior inhalers also produced an aerosol having a cold temperature which was uncomfortable to the patient. Sudden expansion of the liquified propellant/liquid medication mixture upon ejection from the canister resulted in severe cooling of the spray, and severe inertial impaction on the patient's nose and/or throat.
U.S. Pat. No. 4,241,877 to Hughes shows a vortex generating device in FIGS. 5A, 5B, and 6, wherein a gas and a liquid pass into a flow passage together from an inlet. The mixture flows about a rod and forms vortices thereabout and enters a bore along a portion of the rod after which the mixture exits the device through a constricted bore to a semispherical diverging outlet. The liquid is partially atomized as it leaves the bore in the inlet and becomes fully atomized as it leaves the semispherical diverging outlet in a vortical gas stream. A device is also shown where a gas and liquid under pressure are supplied together through an inlet member to a transversely extending rod for formation of vortices. The vortices flow in a direction coaxial with the rod to a constricted outlet bore and to a semispherical diverging outlet. The vortices also flow along auxiliary passages toward the constricted bore portion to combine with the previously-mentioned coaxial flowing vortices.
The Hughes '877 device is suitable for relatively high mass flow rates, but would not be suitable for use with the propellant-charged canisters containing a relatively low propellant-to-medication liquid ratio. With such canisters, it is desirable to minimize the proportion of propellant in each dose and maximize the vortical action of the mixture while flowing through the transducer. Furthermore, it would be difficult and expensive to manufacture a device as indicated in the Hughes '877 patent and still provide the aerosol production capabilities required in conjunction with the propellant-charged canister.
Previous devices also suffered from oropharyngeal drug deposition due to the size and velocity of the aerosol particles. A paper by Martin Tobin, M.D., presented at American Association for Respiratory Therapy, 28th Annual Convention and Exposition, Oct. 30-Nov. 2, 1982, New Orleans, La., describes the various attempts to minimize the oropharyngeal deposition. One device incorporated a cylindrical tube, resulting in a reduction in oropharyngeal deposition. A pear-shaped tube, the design of which was chosen to simulate the shape of an aerosol cloud as it leaves the metered-dose inhaler, did not produce any additional reduction in oropharyngeal drug deposition.
U.S. Pat. Nos. 3,230,924 and 4,190,203 discuss the use of a resonator in conjunction with gas flow. The resonator disclosed in U.S. Pat. No. 4,190,203 assists in atomizing the aerosol produced from the transducer, but is cumbersome.
The present invention overcomes these deficiencies in the prior devices. The present device provides an aerosol delivered at a very small or negligible velocity thereby minimizing the impact of the aerosol on the patient. The device provides a mist having droplets which are uniform in size regardless of the variation in range of pressure provided through the liquified propellant in the canister or the amount of medicament atomized.
A chamber approximately one-fourth the size of the spacer of the prior devices can be used in the present device in order to create the low or zero velocity aerosol. Additionally, the warm temperature of the aerosol is more suitable to the body temperature of the patient for inhalation. The droplets produced by this device are always one to three microns monodispersed as necessary for full and complete penetration of the bronchial tree and the coating of the receptor sites. There is negligible or no deposition in the device itself as diametrically opposed to the prior devices. The performance of prior devices is shown in a paper entitled "Aerosolized Drug Delivery Accessories" by Cutie, et al. in "Aerosol Age", March 1984, which indicates that only 10-15% of the dose "actuated into the respiratory airways" as opposed to over 90% with the present invention.